BEST PRACTICE PROGRAMME GOOD PRACTICE GUIDE 194 GOOD PRACTICE GUIDE 194 Building your own energy efficient house ■ Why save energy ■ How to achieve integrated design ■ Checklist for a low energy home ■ Further information 2001 EDITION 2001 EDITION
BEST PRACTICEP R O G R A M M E
GO
OD
PRA
CT
ICE G
UID
E 194
GOOD PRACTICE GUIDE 194
Building your own energy efficient house
■ Why save energy
■ How to achieve integrated design
■ Checklist for a low energy home
■ Further information
2001 EDITION
2001 EDITION
INTRODUCTION
BUILDING YOUR OWN ENERGY EFFICIENT HOUSE
INTRODUCTION
An energy efficient house will be warm,
comfortable and have low running costs. It will
also cause less damage to the environment. This
Guide introduces the most important concepts to
think about when including energy efficiency
measures into a house design. Energy efficiency
features need not be expensive or use unproven
technology – simple, cheap, tried and tested
measures are often the best. A small additional cost
of around 50p - £1/ft2 (£5-10/m2) is enough to give
a good energy efficient house. With fears of rising
fuel prices and global warming, houses are
becoming more energy efficient. Thinking about
the future when building your house will
go towards providing you with a quality home for
many years to come.
INCLUDING ENERGY EFFICIENCY IN YOUR
HOUSE DESIGN
The best time to include energy efficiency
measures is when a house is being designed and
built. Incorporating energy efficiency from the
beginning will give you maximum benefits for the
least cost. The maximum benefit from energy
efficiency measures will only be obtained from an
integrated approach, ie combining a number of
complementary measures into a comprehensive
package rather than the ad hoc inclusion of single
measures. Use the checklist given in this Guide to
ensure that energy features are fully integrated.
Upgrading the energy efficiency of a house design
need not involve high additional costs.
For example, the extra costs of additional
insulation can be offset against savings from being
able to install a smaller heating system.
For more information on all of the subjects in this
Guide there is a further reading list suggested on
the back page.
STANDARD ASSESSMENT PROCEDURE (SAP)
AND BUILDING REGULATIONS
The SAP is an energy rating which estimates the
space and water heating costs of a house (based
upon its size, heating system and standard
assumptions such as occupancy pattern) and
converts it into a rating on a scale from 1 to 120;
the higher the number, the lower the energy
consumption. The SAP is a useful design tool for
comparing houses and can be used to assess the
benefits of different energy efficiency measures.
The Building Regulations Part L1 (Conservation
of fuel and power) requires basic levels of
insulation. However if it is your intention to
build an energy efficient house then you should
regard these Regulations as an absolute minimum.
Although there are three basic methods for
demonstrating compliance with Part L1, (ask your
architect or package supplier for more information
on this) a high SAP rating will also save effort by
providing most of the information that is needed
to prove compliance.
The fictitious examples on this page (Jones)
and page 3 (Smith) show how SAP ratings can
be used to improve energy efficiency at the
design stage.
CHOOSING YOUR SITE
Using the sun to heat your house saves energy and
makes it more pleasant. If possible choose a site
which allows your house to face south (±45°),
ideally with shelter from prevailing winds, but
without shading to the house. The total window
area shouldn’t be increased, but most of it
should face south to benefit from solar gains.
External blinds can be used to prevent
overheating in summer months. Some windows
will need to face north to ensure good daylight
in all rooms.
The Jones family
The Jones family wanted their
home to have low running costs,
but with little or no additional
build costs.
Their design has:
■ A south-facing orientation
■ Good wall insulation
(U-value of 0.30 W/m2K)
■ 250 mm loft insulation
■ 125 mm floor insulation
■ Double glazing with ‘low-e’
glass + argon
■ ‘A’ rated gas condensing boiler
with radiators
■ Thermostatic radiator valves,
room thermostat and
programmer
■ 50 mm sprayed insulation on
hot water cylinder
SAP = 105
Annual heating and hot water
costs = £246 based on floor
area of 2500 ft2 (232 m2)
1 This applies to England and Wales. Use Part J inScotland and Part F in Northern Ireland. These haveslightly different requirements to Part L1.
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ENERGY SAVING MEASURES
BUILDING YOUR OWN ENERGY EFFICIENT HOUSE
losses and minimises shadowing by other parts
of the house. A bungalow will lose more heat
than a two- or three-storey house of the same
floor area. Rooms which are used most should be
on the south side to take advantage of solar heat
gains. For rooms which are used mostly in the
mornings, such as kitchens and breakfast rooms,
a south-east orientation is best to get full benefit
from the morning sun. Halls, stairs and less
frequently used rooms like bathrooms can go on
the north side.
WINDOWS
Double glazing with ‘low-e’ coating should
be considered a minimum in most new homes.
It reduces heat loss and offers some sound
insulation. Other features such as argon-filled units
and triple glazing are well worth considering.
CONSERVATORIES
Conservatories can help to save energy by reducing
heat losses through adjoining walls (called
buffering) and trapping heat from the sun, but the
savings are small. To be effective they should be on
the south side of the house and not be
overshadowed. Even high quality conservatories
should not have any permanent heating as this
can lead to very high fuel bills, and there should
be double glazed doors to shut them off from the
rest of the house when unused.
HEATING YOUR HOUSE – making the right choices
Low energy houses require smaller and simpler
heating systems than other houses of a similar size,
because heat losses are low. Your choice of heating
system should take into account the availability of
fuels, the time you will spend in your home and its
type of construction.
Ideally, a lightweight construction like timber
frame should be matched with a responsive
heating system which is quick to supply heat
where and when it is needed.
An example would be a warm air system or radiators
with thermostatic radiator valves (TRVs), installed in
a timber frame house which is occupied morning
and evening. Underfloor and other ‘storage’
Unlike the Jones family the Smiths
did not specify energy efficiency,
so their house was
only designed to meet the
minimum requirements of the
Building Regulations.
Their design has:
■ Basic wall insulation
(U-value of 0.35 W/m2K)
■ 250 mm loft insulation
■ 80 mm floor insulation
■ Double glazing with
‘low-e’ glass
■ ‘D’ rated gas boiler with
radiators
■ Thermostatic radiator valves,
room thermostat and
programmer
■ 30 mm sprayed insulation on
hot water cylinder
SAP = 94
Annual heating and hot water
costs = £309 based on floor
area of 2500 ft2 (232 m2)
The Smith family INSULATION
A large part of the heat lost from a house is through
the walls. Whichever method of construction you
choose, building in insulation is the easiest and
cheapest way of improving energy efficiency.
Standard timber frame walls (90 mm) can easily be
upgraded by specifying 140 mm studs which allow
more insulation, and masonry walls can be
improved using fully filled 100 mm cavities and
lightweight ‘thermal’ blocks. Both of these will give
a U-value better than 0.30 W/m2K. (The U-value is
a measure of the thermal performance of part of the
building. The lower the better.) For severe weather
locations where fully filled cavities are not suitable,
partially filled cavities can be used.
Lofts should have at least 250 mm of insulation:
100 mm laid between the joists and 150 mm laid
across them. This gives a U-value of 0.16 W/m2K.
Rooms in the roof and dormer windows need
careful attention to detail but can also be insulated
to a high standard. Ground floor heat loss
calculations are more difficult and there are many
different types of floors, but all are easily insulated
during construction. A layer of 125 mm
polystyrene (or equivalent) is recommended, but
for underfloor heating, increase the insulation to
minimise the heat losses to the ground.
HOUSE LAYOUT
When thinking about the design of your house,
remember, a compact plan without ‘extensions’
minimises the external wall area, reduces heat
3
ENERGY SAVING MEASURES AND SITE PRACTICE
BUILDING YOUR OWN ENERGY EFFICIENT HOUSE
systems are less suited to very lightweight
constructions as they cannot generally respond
as quickly.
As wet underfloor systems can have radiators
as well as underfloor heating circuits, a
combination of underfloor heating in the
downstairs rooms and radiators elsewhere is
a worthwhile compromise. A tiled solid screed
floor works best with underfloor heating and
rugs, instead of fitted carpet. Condensing
boilers, have efficiencies up to 90% and are
more efficient than conventional boilers. They
can be used in place of an ordinary boiler for
both radiators and underfloor heating, the
only difference being the need for a small
outlet to the drainage system for the condensed
flue gases.
If you want a focal fire then multi-fuel stoves are a
good option especially if you are able to take
advantage of free fuel such as wood. These are also
much more efficient than open fires, and won’t
give such high heat losses through the
flue from increased ventilation when they are
not being used.
Hot water efficiency is governed largely by the
efficiency of the boiler rather than the type
of hot water system, eg mains pressure,
unvented etc, but the more insulation around
the store the better (50 mm plus). Good controls
are important to maximise the efficiency of
a heating system and are required to comply
with Building Regulations. Individual room
control is particularly important in rooms with
large south-facing windows. If your house will
have two or more distinct parts which will be
used at different times, eg an annexe or office,
zone controls may be worth considering. Choose
controls that are easy to use and fit them where
they are easily accessible.
VENTILATION
Ventilation is important to provide fresh air and
prevent condensation. There must be extract
fans or passive stack ventilation (PSV) in
kitchens and bathrooms to satisfy Building
Regulations. PSV uses the principle of rising
warm air to extract without the need for electric
fans. Permanent ventilation must also be
provided to all other rooms using ‘trickle vents’.
Draught lobbies (unheated) on main entrances
help reduce heat losses and are recommended.
Mechanical ventilation with heat recovery may
offer benefits such as filtered air and reduced
noise intrusion. However, they should not
generally be seen as an energy efficiency feature
since the cost of the electricity used to run
fans often outweighs the benefits from the heat
recovery. They also need a well sealed house
to work efficiently – no open chimneys or flues.
LIGHTING
Maximising daylighting and good lighting
design, combined with the use of compact or
strip fluorescent lights, will save considerable
amounts on running costs. Fluorescent lamps
also have a much longer life than ordinary light
bulbs. The most important places to fit them are
where lights are left on for long periods, eg
outside light, halls and stairs, and main
living areas.
BRIEFING DESIGNERS
Many architects and designers will be aware of
energy efficient principles, but often they will be
designing homes that don’t go beyond Building
Regulations. You don’t need to specify fine
details to achieve an energy efficient design.
Instead, give the designer a target to work to –
perhaps improving the initial design by 10 SAP
points, setting maximum running cost or
U-value targets. To help achieve an energy
efficient design:
■ Choose an architect or package supplier who
has knowledge of low energy design
■ Provide references for low energy techniques
and measures
■ Discuss your aims and reasons for wanting a
low energy design
■ Provide a target SAP energy rating
or running cost
■ Explain how you will use your house,
eg all day or morning and evening
SITE PRACTICE
Good site supervision and
proper materials storage are
critical to the success of
energy efficiency measures.
Potential problems such as
gaps in insulation
materials or damaged
double glazed units can be
easily overcome with
careful supervision during
building. If you are
managing the project
yourself, pay particular
attention to details like
insulation junctions and
where services enter the
house. Insulation should be
kept dry to avoid damage
and prolonging the drying
out period.
4
A CHECKLIST FOR A LOW ENERGY HOME
BUILDING YOUR OWN ENERGY EFFICIENT HOUSE
Orientate your house towards south
Locate most windows on the south side and reduce size of north-facing windows
Place living rooms and main bedrooms on the south side
Install a responsive heating system and controls
Maximise solar heating:
Choose an architect or package supplier with knowledge of and enthusiasm for low energy design
Brief builders on the low energy aim of your house
Select tradespeople with knowledge and experience of energy efficiency
Get the right team:1
Size the system correctly
Fit condensing boilers (oil or gas) where possible
Install good, easy-to-use controls
Install an efficient heating and hot water system:4Overlap insulation between elements eg between loft and walls
Keep cavities clear of debris
Don’t compress insulation materials
Keep insulation materials dry
Seal holes where services enter your house
Ensure the success of energy measures:5
Make sure you understand the heating system
Set heating controls to suit your needs
Fit low energy lights
Allow the house to dry out - particularly masonry houses
Buy low energy appliances
Avoid permanent shading, such as net curtains, that stop solar gains
And when moving in:
Design a compact house plan
Ensure high levels of insulation in all external elements (including windows)
Provide controlled ventilation
Draughtstrip all external openings
Ask your architect for energy calculations eg expected fuel bills
Minimise heat losses:2
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